Xerodin

Veterans were also victims of the orphan crushing machine, usually recruited from impoverished areas with the promise of a stable job, health care, and education. They were once broke high school kids from podunk towns with zero opportunities for upward mobility. I think the left in America is missing a huge opportunity to take advantage of the fetishization of veterans. A few charismatic veterans who espouse a leftist platform can lend a lot of pathos for the cause from the view of the average ‘red-blooded American.’

The second sentence of the Wikipedia article literally says about 2/3 were American citizens.

The section on ‘Exclusion, removal, and detention’ says “[s]omewhere between 110,000 and 120,000 people of Japanese ancestry were subject to this mass exclusion program, of whom about 80,000 Nisei (second generation) and Sansei (third generation) were U.S. citizens.”

So yes, second and third generation Japanese Americans, natural born citizens, were held in American concentration camps.